<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

    <style>
        .Site {
            display: flex;
            min-height: 100vh;
            flex-direction: column;
        }
        
        .Site-content {
            flex: 1;
        }
    </style>
</head>

<body>

    <body class="Site">
        <header>...</header>
        <main class="Site-content">...</main>
        <footer>...</footer>
    </body>
</body>

</html>